Description of the Conventional Art
A conventional phase change material may transition between a crystalline state and an amorphous state according to temperature. The resistance of a phase change material in a crystalline state is lower than that in the amorphous state. The crystalline state and the amorphous state of the phase change material may be reversible. When a phase change material is applied to a memory device, the device is referred to as a phase change memory device
A conventional phase change memory device may include a phase change material layer electrically connected to a source region or drain region of a transistor via a contact plug. The phase change memory device may be driven using a resistance difference resulting from a crystalline state change of the phase change material layer.
In a conventional manufacturing process, a storage node may be formed by sequentially etching an upper electrode and the phase change material layer after sequentially depositing the phase change material layer and the an upper electrode.
During a conventional manufacturing process, however, when etching the phase change material layer, a side of the phase change material layer may be damaged and the damage may affect the characteristics of the conventional phase change memory device. For example, an etching gas may penetrate into a relatively weak phase change material layer and an interface there below, which may negatively affect a program volume of the phase change material layer.
In another conventional phase change memory device, a relatively limited structure in which a phase change material layer is formed in a contact hole may have a lower reset current. In this conventional phase change memory device, an opening of the contact hole may be inhibited or blocked by an overhang while forming the phase change material layer within the contact hole. Accordingly, a seam or void may be formed in the phase change material layer. The seam or the void in the phase change material layer may increase a set resistance of the phase change material layer. Additionally, the size and shape of the seam or void may vary according to the difference of a contact hole profile of each cell. This may result in relatively large deviations in set resistance, reset resistance and/or a reset current between cells.